This project proposes a neurophysiological and neuropharmacological study of the caudate nucleus in a model of Parkinson's disease produced by the interruption of the nigrostriatal pathway in cats. We intend to compare the effects of acetylcholine, dopamine, serotonin, GABA and other drugs with the effects of stimulating different fiber systems converging on this nucleus. We thereby wish to test the hypotheses that the normal functioning of the caudate nucleus depends on a balance between cholinergic, dopaminergic and serotoninergic inputs and that Parkinson's disease is due to a disturbance of this balance. We will use multibarreled micropipettes in order to apply drugs microiontophoretically near single neurons of the caudate nucleus and to record the spontaneous firing and the synaptic responses of these neurons. The neuronal responses will be enhanced by the computation of post-stimulus histograms and of average focal evoked potentials. BIBLIOGRAPHIC REFERENCES: Stahl, S.M., Daniels, A.C., Derda, D. and Spehlmann, R.: Injection of 6-hydroxydopamine and hydrogen peroxide into the substantia nigra and lateral ventricle of the cat: specific and nonspecific effects on striatal biogenic amines. J. Neurochem. 24: 165-172, 1975. Spehlmann, R.: The susceptibility to acetylcholine and dopamine of neurons in the caudate nucleus of cats with chronic nigrostriatal lesions. Trans. Amer. Neurol. Ass. 99: 61-63, 1975.